A 48-year-old man with pemphigus vulgaris has been on prednisolone 40 mg/day for 6 weeks with excellent clinical response (no new blisters, healing of existing lesions). To minimize long-term corticosteroid toxicity and maintain remission, which steroid-sparing agent is most appropriate to add now?

Explanation

## Steroid-Sparing Agents in Pemphigus Vulgaris **Key Point:** Azathioprine is the most widely used and first-choice steroid-sparing agent in pemphigus vulgaris. It is added after 2–4 weeks of systemic corticosteroid induction to allow gradual steroid dose reduction while maintaining disease control. ### Why Azathioprine is Preferred 1. **Mechanism**: Purine analog that inhibits T-cell and B-cell proliferation, reducing anti-desmoglein antibody production. 2. **Efficacy**: Reduces cumulative corticosteroid dose by 50–70% and allows tapering to maintenance doses (5–10 mg/day). 3. **Evidence**: Gold standard steroid-sparing agent in all major guidelines; most extensive clinical experience in pemphigus. 4. **Cost-effectiveness**: Significantly cheaper than rituximab or mycophenolate mofetil. ### Typical Dosing and Monitoring - **Initial dose**: 1–2 mg/kg/day (typically 50–100 mg/day). - **Onset of action**: 6–8 weeks; therefore added early while corticosteroids are still effective. - **Monitoring**: TPMT testing before initiation; CBC and LFTs every 4 weeks initially, then every 3 months. - **Adverse effects**: Bone marrow suppression (rare), hepatotoxicity, pancreatitis, increased infection risk. ### Comparison of Steroid-Sparing Agents in Pemphigus | Agent | Onset | Efficacy | Monitoring | First-Line? | | --- | --- | --- | --- | --- | | Azathioprine | 6–8 weeks | High | CBC, LFTs, TPMT | **Yes** | | Mycophenolate mofetil | 4–6 weeks | High | CBC, LFTs | Alternative | | Rituximab (anti-CD20) | 2–4 weeks | Very high | CD19+ count, immunoglobulins | Refractory only | | Cyclosporine | 2–4 weeks | Moderate | Trough levels, renal function, BP | Not preferred (nephrotoxicity) | | Dapsone | 1–2 weeks | Low | G6PD, CBC | Not for PV (for linear IgA) | **High-Yield:** The combination of prednisolone + azathioprine allows steroid tapering to 5–10 mg/day maintenance within 3–6 months, compared to 20–30 mg/day if corticosteroids are used alone [cite:Dermatology Textbook]. **Clinical Pearl:** Azathioprine should be started early (week 2–4 of corticosteroid therapy), not delayed until steroid toxicity develops, because its slow onset (6–8 weeks) requires overlap with systemic corticosteroids. **Mnemonic:** **AZAT** = **A**zathioprine is the **A**djunct of choice, **T**iming is early (week 2–4), **A**ction takes 6–8 weeks, **T**herapy is combined with corticosteroids. **Warning:** Dapsone is NOT used in pemphigus vulgaris; it is indicated for linear IgA disease and dermatitis herpetiformis. Cyclosporine causes nephrotoxicity and hypertension, making it less preferred despite faster onset.